1991 300 zx speedometer and odometer don't work.

The cruise control, speedometer/odometer will not work without a functioning speed sensor, if you have replace the speed sensor then you could have wiring or computer issues. These old Nissan OBD 1 systems were a hassle to diagnose properly, even the dealers had fits with them.

The first thing to find out is if you have an electronic or mechanical speedometer. A mechanical speedometer will have a cable going from the back of the instrument cluster down to the transmission. The 18 year old "tech" will have no idea what he's looking at! This cable screws into the transmission. As you drive the gear that the cable is screwed into spins, the cable spins, and a magnetic cup in the instrument cluster spins. The speedometer needle is attached to the magnet and is positioned on the dial by how fast the magnetic is spinning. Most likely the cable is broken inside the housing or the gear in the transmission is stripped. It's made of plastic. If you have an electronic speedometer the stepper motor that positions the needle and runs the odometer wheels is probably worn out. So in this case replacing the instrument cluster should fix it. Hope that helps! Jim